Prioritized common subframe to provide better service to the overlapping areas in a community

ABSTRACT

A subframe structure for a wireless community uses a master common subframe and second master common subframe method to give BSs different priorities to serve overlapping areas in common subframes. The subframe structure and corresponding method can increase overlapping cells&#39; capacity and reduce interference.

RELATED APPLICATION

The present application claims the benefit of U.S. Provisional PatentApplication No. 60/891,122 filed on Feb. 22, 2007, which is herebyincorporated in its entirety by reference for all purposes as if fullyset forth herein.

BACKGROUND OF THE INVENTION

The present invention relates to wireless networks and, morespecifically, to a method for addressing and minimizing interference dueto overlapping wireless systems.

The 802.16h draft standard suggests two kinds of subframe structureswhich allocate for each system a period of time during which it isguaranteed interference free operation. During this interval, called themaster system, no other system (slave system) is allowed to interfere.However, the other systems are allowed to operate in areas where they donot cause interference to the master system, thus improving the capacityof those slave systems, which would otherwise have to be totally silent.

FIG. 1 shows the interference due to overlapping systems when all thethree systems have the same working channel. Three base stations S1, S2,and S3 are shown in FIG. 1. Single coverage areas include Xcorresponding to base station S1, Y corresponding to base station S2,and Z corresponding to base station S3. Dual coverage areas include Acorresponding to base stations S1 and S2, B corresponding to basestations S1 and S3, and C corresponding to base stations S2 and S3. Atriple coverage area D corresponds to all three base stations S1, S2,and S3.

FIG. 2 describes a first subframe structure of the community containingthese three overlapping systems shown in FIG. 1. FIG. 2 shows a commonsubframe that is part of the MAC Frame when all the systems of acoexistence community may operate in parallel. The operation duringthese subframes may require limitations of the transmit power. FIG. 2also shows a master subframe that is part of the MAC frame used by aspecific system (master system) of a coexistence community to operatewith reduced interference from its neighboring systems. FIG. 2 alsoshows a slave subframe that is part of the MAC frame coinciding with themaster subframe in which all systems (other than the master) of thecoexistence community have restricted operation.

FIG. 3 shows an alternative subframe structure of the communitycontaining the three overlapping systems. The difference between FIGS. 2and 3 is that in FIG. 2 each frame includes a master subframe of eachcell in a community operating in the same working channel, whereas inFIG. 3 each frame includes a master subframe of only one cell in acommunity operating in the same working channel. This means that in FIG.3 three frames are required to provide master subframes of the cells ina community with three cells operating in the same working channel. Bothof the subframe structures of FIGS. 2 and 3 are known to those skilledin the art.

In a common subframe, the Base Station (“BS”) provides service to theSubscriber Station(s) (“SSs”) located in a non-overlapping area. In amaster subframe, the BS has priority over the other systems which meansit can service all the SSs associated with it. In a slave subframe, theBS should not interfere with the BS in a master state, which means itcan provide service to the SSs in the non-overlapping area. FIG. 4illustrates the regions being served during the various subframes whenthe subframe structure of FIG. 3 is used.

Note that in FIG. 4, Region X, which is served by base station S1,without any interference from base station S2 and S3, is served duringall the subframes. An SS located in that region is served during thecommon frames as well as during the subframes in which S1 is either aslave or a master. Similarly, SSs located in regions Y and Z are alsoserved by either S2 or S3 during all the subframes, as can be seen inFIG. 4.

On the other hand, S1 SSs located in region A suffer from interferencefrom base station S2, consequently they are not served during the commonsubframes but only when S1 is the master. When S2 is the master, itserves all its SSs located in region A. When S3 is the master, area Acan not be served by either S1 or S2 since no priority is allocated toeither of them. Similarly, SSs in areas B and C should be served onlyduring the master subframes of their corresponding system. In a commonsubframe, SSs in areas A, B, C, and D can not be served by any BS sinceno priority is allocated to any BS.

A slave hierarchy method has been proposed to give SSs in overlappingareas more chance to be served. The idea behind the method is to definea certain slave hierarchy. For example, after being the master a systembecomes a “secondary master” and still has priority over all othersystems in the neighborhood except the new master. Thus in the secondsubframe, base station S2 is the master, but base station S1 is now the“secondary master” and has priority over base station S3, in the thirdsubframe, base station S3 becomes the master, while base station S2, the“secondary master,” has priority over base station S1. In the fourthsubframe, again base station S1 is the master, while base station S3 isthe second master.

Accordingly, a first new subframe structure is defined in FIG. 5 and asecond new subframe structure is defined in FIG. 6. FIG. 5 shows asubframe structure with slave hierarchy including a common frame,master, secondary master, and slave for each of base stations S1, S2,and S3. FIG. 6 shows a subframe structure with slave hierarchy includinga common frame/master, common frame/secondary master, and commonframe/slave for each of base stations S1, S2, and S3. The differencebetween FIGS. 5 and 6 is that in FIG. 5 each frame includes a mastersubframe and secondary master of each cell in a community operating inthe same working channel, whereas in FIG. 6 each frame includes a mastersubframe of only one cell and a secondary master subframe in a communityoperating in the same working channel. This means that in FIG. 6, threeframes are required to provide master subframes of the cells andsecondary master subframes in a community with three cells operating inthe same working channel.

FIG. 7 shows the regions being served during the various subframes whenthe subframe structure of FIG. 6 with slave hierarchy is used.

As shown in FIG. 7, during the 3^(rd) subframe base station S2 is thesecondary master and has priority over base station S1, and the SSs inarea A can be served. Similarly, S1 SSs in area B can be served duringthe second subframe and S3 SSs in area C can be served during the firstsubframe.

After this optimization, SSs in areas A, B, C, and D still can not beserved by any BS since no priority is allocated to any BS in a commonsubframe. What is desired, therefore, is a further optimization toaddress this problem of the prior art.

SUMMARY OF THE INVENTION

According to the present invention, a subframe structure with slavehierarchy uses a prioritized common subframe to substantially reduceinterference and to provide better service in overlapping areas of awireless community.

The 802.16h draft introduces subframe structure (common subframe, mastersubframe/slave subframe) to harmonize the frame transmissions of theoverlapping BSs working in the same channel (these BSs are defined as acommunity). The prior art introduces hierarchy slave subframes to makespecial reuse more efficient. According to the present invention, twocommon subframe optimizations are set forth to provide even furtherreduction of interference and greater service in overlapping areas ofthe wireless community.

According to a first embodiment of the invention, a first subframestructure uses a master/slave common subframe. The BS in the mastercommon subframe has priority over all the other BSs in a community thatcan communicate with SSs in an overlapping area. But if a BS in theslave common subframe asks the BS in the master common subframe todecrease transmission power or use the slave common subframe, the BS inthe master common subframe should follow the indication.

According to a second embodiment of the invention, a second subframestructure uses a second master common subframe. The BS in the secondmaster common subframe has priority over all other systems except the BSin the master common subframe. The BS in the second master commonsubframe can service the area that is overlapping with the BS in theslave common subframe. But if a BS in the slave common subframe asks theBS in the second master common subframe to decrease transmission poweror go to the slave common subframe, the BS in the second master commonsubframe should follow the indication.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned and other features and objects of the presentinvention and the manner of attaining them will become more apparent,and the invention itself will be best understood, by reference to thefollowing description of a preferred embodiment taken in conjunctionwith the accompanying drawings, wherein:

FIG. 1 is a diagram showing interference due to overlapping wirelesssystems;

FIG. 2 shows a first subframe structure according to the prior art;

FIG. 3 shows a second subframe structure according to the prior art;

FIG. 4 shows regions being served during the various subframes using thesubframe structure of FIG. 3;

FIG. 5 shows a first subframe structure with slave hierarchy accordingto the prior art;

FIG. 6 shows a second subframe structure with slave hierarchy accordingto the prior art;

FIG. 7 shows regions being served during the various subframes using thesubframe structure of FIG. 6 with slave hierarchy;

FIG. 8 shows a first subframe structure with master/slave common frameoptimization according to the present invention;

FIG. 9 shows a second subframe structure with master/slave common frameoptimization according to the present invention;

FIG. 10 shows regions being served during the various subframes usingthe subframe structure of FIG. 9 with a master common frame;

FIG. 11 shows a first subframe structure with master/second mastercommon frame optimization according to the present invention;

FIG. 12 shows a second subframe structure with master/second mastercommon frame optimization according to the present invention; and

FIG. 13 shows regions being served during the various subframes usingthe subframe structure of FIG. 12 with a master/second master commonframe.

DETAILED DESCRIPTION OF THE INVENTION

An optimized subframe structure for a wireless community according to afirst embodiment of the invention using a master/slave common subframe(M-C-subframe/S-C-subframe) is described below with reference to FIGS.8-10.

In order to allow a system to serve SSs in overlapping areas in commonsubframes, a common subframe priority is provided according to a firstembodiment of the invention: master common subframe (M-C-subframe) andslave common subframe (S-C-subframe). In the M-C-subframe, the BS hasthe master role which may use its maximum capable and allowed operatingEquivalent Isotropically Radiated Power (“EIRP”) to serve all SSsassociated with it if no other BS is interfered with by the BS in theM-C-subframe. If the BS in the M-C-subframe receives requests from itsneighbor BSs to ask it to decrease its transmission power or use theS-C-subframe, it should follow the request.

In the S-C-subframe, the BS has the slave role to service thenon-overlapping area. If a BS in the S-C-subframe detects interferencefrom the BS in the M-C-subframe, it may request the BS in theM-C-subframe to decrease the transmission power until the BS in theM-C-subframe does not interfere with it. Or this BS may request the BSin the M-C-subframe to use the S-C-subframe.

After this optimization, subframe structure 1 is shown in FIG. 8 andsubframe structure 2 is shown in FIG. 9.

FIG. 8 shows a first subframe structure with master/slave common frameoptimization according to the first embodiment of the invention. In afirst frame N base station S1 includes, in order, a master commonsubframe, a master subframe, a secondary master subframe, and a slavesubframe. Base station S2 includes, in order, a slave common subframe, aslave subframe, a master subframe, and a secondary master subframe. Basestation S3 includes, in order, a slave common subframe, a secondarymaster subframe, a slave subframe, and a master subframe. In a secondframe N+1, base station S1 includes, in order, a slave common subframe,a master subframe, a secondary master subframe, and a slave subframe.Base station S2 includes, in order, a master common subframe, a slavesubframe, a master subframe, and a secondary master subframe. Basestation S3 includes, in order, a slave common subframe, a secondarymaster subframe, a slave subframe, and a master subframe. In a thirdframe N+2, base station S1 includes, in order, a slave common subframe,a master subframe, a secondary master subframe, and a slave subframe.Base station S2 includes, in order, a slave common subframe, a slavesubframe, a master subframe, and a secondary master subframe. Basestation S3 includes, in order, a master common subframe, a secondarymaster subframe, a slave subframe, and a master subframe.

FIG. 9 shows a second subframe structure with master/slave common frameoptimization according to the first embodiment of the present invention.In frame N, base station S1 includes a master common subframe and amaster subframe, base station S2 includes a slave common subframe and aslave subframe, and base station S3 includes a slave common subframe andsecondary master subframe. In frame N+1, base station S1 includes aslave common subframe and a secondary master subframe, base station S2includes a master common subframe and a master subframe, and basestation S3 includes a slave common subframe and slave subframe. In frameN+2, base station S1 includes a slave common subframe and a slavesubframe, base station S2 includes a slave common subframe and asecondary master subframe, and base station S3 includes a master commonsubframe and master subframe.

FIG. 10 shows the regions being served during the various subframes whenthe second subframe structure of FIG. 9 with the master common subframeis used.

After the first optimization scheme described above, there are stillsome areas that can not be served by any BS in the common subframe. WhenS3 is in the master common subframe, area A can not be served by eitherS1 or S2 since no priority is allocated to either of them. When S1 is inthe master common subframe, area C can not be served by either S2 or S3since no priority is allocated to either of them. Similarly, when S2 isin the master common subframe, area B can not be served by either S1 orS3 since no priority is allocated to either of them.

An optimized subframe structure for a wireless community according to asecond embodiment of the invention using a slave hierarchy commonsubframe is described below with reference to FIGS. 11-13.

A hierarchy method according to the second embodiment of the inventionuses a slave common subframe to give SSs in overlapping areas morechance to be served. The method of the second embodiment of theinvention defines a certain slave hierarchy. For example, after havingthe master common subframe a system has a “second master” commonsubframe (S-M-C-subframe) and still has priority over the other systemsin the neighborhood except the system having the new master commonsubframe (M-C-subframe).

If a BS using the S-M-C-subframe receives requests from its neighbor BSto ask it to decrease its transmit power or use the slave commonsubframe (S-C-subframe), it should follow these requests.

FIG. 11 shows the first subframe structure with master/second mastercommon frame optimization according to the second embodiment of theinvention. In a first frame N, base station S1 includes, in order, amaster common subframe, a master subframe, a secondary master subframe,and a slave subframe. Base station S2 includes, in order, a slave commonsubframe, a slave subframe, a master subframe, and a secondary mastersubframe. Base station S3 includes, in order, a secondary master commonsubframe, a secondary master subframe, a slave subframe, and a mastersubframe. In a second frame N+1, base station S1 includes, in order, asecondary master common subframe, a master subframe, a secondary mastersubframe, and a slave subframe. Base station S2 includes, in order, amaster common subframe, a slave subframe, a master subframe, and asecondary master subframe. Base station S3 includes, in order, a slavecommon subframe, a secondary master subframe, a slave subframe, and amaster subframe. In a third frame N+2, base station S1 includes, inorder, a slave common subframe, a master subframe, a secondary mastersubframe, and a slave subframe. Base station S2 includes, in order, aslave common subframe, a slave subframe, a master subframe, and asecondary master subframe. Base station S3 includes, in order, a mastercommon subframe, a secondary master subframe, a slave subframe, and amaster subframe.

FIG. 12 shows a second subframe structure with master/second mastercommon frame optimization according to the second embodiment of theinvention. In frame N, base station S1 includes a master common subframeand a master subframe, base station S2 includes a slave common subframeand a slave subframe, and base station S3 includes a secondary mastercommon subframe and secondary master subframe. In frame N+1, basestation S1 includes a secondary master common subframe and a secondarymaster subframe, base station S2 includes a master common subframe and amaster subframe, and base station S3 includes a slave common subframeand slave subframe. In frame N+2, base station S1 includes a slavecommon subframe and a slave subframe, base station S2 includes asecondary master common subframe and a secondary master subframe, andbase station S3 includes a master common subframe and master subframe.

FIG. 13 describes regions being served during the various subframes whenthe second subframe structure with master/second master common subframeshown in FIG. 12 is used. Note that in FIG. 13, all of the overlappingareas A, B, C, and D, can now be serviced using the subframe structureof the second embodiment of the present invention and none are blocked.Thus, the subframe structure of the second embodiment of the presentinvention greatly improves services in the overlapping areas and reducesinterference.

Glossary

-   Subscriber Station (SS): A generalized equipment set providing    connectivity between subscriber equipment and a base station (BS).-   Frame: A structured data sequence of fixed duration used by some PHY    (Physical Layer Specification) specifications. A frame may contain    both an uplink subframe and a downlink subframe. The downlink    subframe is used for transmitting data from a BS (base station) to    its associated SSs. The uplink subframe is used for transmitting    data from SSs to the BS with which they associate.-   Common subframe: That part of the MAC (Media Access Control) frame    when all the systems of a coexistence community may operate in    parallel. The operation during these subframes may require    limitations of the transmit power.-   Master subframe: That part of the MAC frame which is used by a    specific system (master system) of a coexistence community to    operate with reduced interference from its neighboring systems.-   Slave subframe: That part of the MAC frame coinciding with the    master subframe in which all systems (other than the master) of the    coexistence community have restricted operation.-   MAP: A set of information that defines the entire access for a    scheduling interval. There are two kinds of MAPs: downlink map    (DL-MAP) and uplink map (UL-MAP).

While there have been described above the principles of the presentinvention in conjunction with specific memory architectures and methodsof operation, it is to be clearly understood that the foregoingdescription is made only by way of example and not as a limitation tothe scope of the invention. Particularly, it is recognized that theteachings of the foregoing disclosure will suggest other modificationsto those persons skilled in the relevant art. Such modifications mayinvolve other features which are already known per se and which may beused instead of or in addition to features already described herein.Although claims have been formulated in this application to particularcombinations of features, it should be understood that the scope of thedisclosure herein also includes any novel feature or any novelcombination of features disclosed either explicitly or implicitly or anygeneralization or modification thereof which would be apparent topersons skilled in the relevant art, whether or not such relates to thesame invention as presently claimed in any claim and whether or not itmitigates any or all of the same technical problems as confronted by thepresent invention. The applicant hereby reserves the right to formulatenew claims to such features and/or combinations of such features duringthe prosecution of the present application or of any further applicationderived therefrom.

1. A subframe structure for a wireless community comprising a master andslave common subframe.
 2. The subframe structure of claim 1 wherein abase station in the master common subframe has priority over all of theother base stations in the wireless community that can communicate withsubscriber stations in an overlapping area.
 3. The subframe structure ofclaim 2 wherein if a base station in a slave common subframe asks a basestation in the master common subframe to decrease transmission power,the base station in the master common subframe should follow theindication.
 4. The subframe structure of claim 2 wherein if a basestation in a slave common subframe asks a base station in the mastercommon subframe to use a slave common subframe, the base station in themaster common subframe should follow the indication.
 5. The subframestructure of claim 1 further comprising a master subframe, a secondarymaster subframe, and a slave subframe.
 6. A method for improving theservice and reducing interference in a wireless community comprisingusing a common subframe including a master common subframe and a slavecommon subframe.
 7. The method of claim 6 wherein a base station in themaster common subframe has priority over all of the other base stationsin the wireless community that can communicate with subscriber stationsin an overlapping area.
 8. The method of claim 7 wherein if a basestation in a slave common subframe asks a base station in the mastercommon subframe to decrease transmission power, the base station in themaster common subframe should follow the indication.
 9. The method ofclaim 7 wherein if a base station in a slave common subframe asks a basestation in the master common subframe to use a slave common subframe,the base station in the master common subframe should follow theindication.
 10. The method of claim 6 further comprising the use of amaster subframe, a secondary master subframe, and a slave subframe. 11.A subframe structure for a wireless community comprising a mastercommon, second master common, and a slave common subframe.
 12. Thesubframe structure of claim 11 wherein a base station in the secondmaster common subframe has priority over all of the other base stationsin the wireless community that can communicate with subscriber stationsin an overlapping area except for the base station in the master commonsubframe.
 13. The subframe structure of claim 12 wherein if a basestation in a slave common subframe asks a base station in the secondmaster common subframe to decrease transmission power, the base stationin the second master common subframe should follow the indication. 14.The subframe structure of claim 12 wherein if a base station in a slavecommon subframe asks a base station in the second master common subframeto use a slave common subframe, the base station in the master commonsubframe should follow the indication.
 15. The subframe structure ofclaim 11 further comprising a master subframe, a secondary mastersubframe, and a slave subframe.
 16. A method for improving the serviceand reducing interference in a wireless community comprising using acommon subframe including a master common, a second master common, and aslave common subframe.
 17. The method of claim 16 wherein a base stationin the second master common subframe has priority over all of the otherbase stations in the wireless community that can communicate withsubscriber stations in an overlapping area except for the base stationin the master common subframe.
 18. The method of claim 17 wherein if abase station in a slave common subframe asks a base station in thesecond master common subframe to decrease transmission power, the basestation in the second master common subframe should follow theindication.
 19. The method of claim 17 wherein if a base station in aslave common subframe asks a base station in the second master commonsubframe to use a slave common subframe, the base station in the mastercommon subframe should follow the indication.
 20. The method of claim 16further comprising the use of a master subframe, a secondary mastersubframe, and a slave subframe.